Did Solar Energetic Particles Produce the Short‐lived Nuclides Present in the Early Solar System?

Abstract

Production of the short-lived nuclides 41Ca, 36Cl, 26Al, and 53Mn by solar energetic particles (SEP) interacting with dust grains of chondritic (\solar) composition is estimated considering a broad range of spectral parameters for the SEP and appropriate nuclear reaction cross sections. The dust grains are assumed to follow a power-law size distribution and to range in size from 10 km to 1 cm. The possibility that an enhanced Ñux of SEP from an active early (T Tauri) Sun could have been responsible for the production of these short-lived nuclides in the early solar system is investigated. SEP production of 41Ca and 36Cl will match their abundances in the early solar system inferred from meteorite data if the SEP irradiation duration was D 5 ] 105È106 yr and the SEP Ñux was higher by a factor of more than 5 ] 103 than the contemporary long-term averaged value of (E [ 10 MeV) D 100 cm~2 s~1. N proton However, corresponding production of 26Al will be much below the level needed to match its inferred abundance in the early solar system. SEP production, therefore, fails to explain the observed correlated presence of 41Ca and 26Al with canonical initial abundances in early solar system solids. The abundance of 53Mn in the early solar system is not tightly constrained by the meteorite data, and the various estimates di †er by a factor of 5. Coproduction of 41Ca, 36Cl, and 53Mn that will match the meteorite data for the higher initial abundance of 53Mn is possible if the SEP irradiation persisted for about a million years or more with a Ñux enhancement factor of D 5000È10,000. On the other hand, the lower initial value of 53Mn can also be matched by a Ñux enhancement factor of D1000 and an irradiation duration of a few million years ; the corresponding production of the other nuclides will be ¹10% of the level needed to match their abundances in the early solar system. Target abundance consideration rules out the possibility of SEP production of 60Fe, another short-lived nuclide present in the early solar system. Thus, SEP production as the primary source of the short-lived nuclides in the early solar system appears to be unlikely. However, the possibility that SEP production could be an important source of 53Mn as well as of the short-lived nuclide 10Be, whose presence in the early solar system solids has been recently reported, makes it difficult to completely rule out any contribution from this source to the inventory of these nuclides in the early solar system.

The Irradiation Origin of Beryllium Radioisotopes and Other Short‐lived Radionuclides

“…These quantities can vary over many orders of magnitude, depending on the astrophysical environment, implying changes in the short-lived-radionuclide yields of many orders of magnitude. Other parameters, like the composite structure of the targets, the shielding, or the cosmicray properties, induce variations in the yields of the short-lived radionuclides that are no larger than a few orders of magnitude (Lee et al 1998;Goswami et al 2001;Gounelle et al 2001;Marhas et al 2002;Leya et al 2003). …”

“…More recently, an Orion-like environment has been suggested for the birth of the solar system (Hester et al 2004). The internal irradiation model conjectures that the radionuclides were created by the irradiation of the solar environment by energetic protons and 4 He and 3 He nuclei, accelerated by gradual or impulsive events near an active young Sun (Lee et al 1998;Goswami et al 2001;Gounelle et al 2001;Marhas et al 2002;Leya et al 2003). Thus, establishing the origin of the short-lived radionuclides can provide important constraints on the astrophysical setting of the Sun's birth, stellar nucleosynthesis models, irradiation processes around young stellar objects, and early solar system chronology (Gounelle & Russell 2005a, 2005bKita et al 2005).…”

The weak-line T Tauri star V410 Tau

“…Although external phenomena, like supernova explosions, have been used to explain these abundances, it has been suggested that they could also be due to spallation reactions from energetic (MeV) protons and ions originating in magnetic reconnection flares (see also Goswami et al 2001;Marhas et al 2002;Leya et al 2003).…”

Energetic Constraints on In Situ Production of Short-Lived Radionuclei in the Early Solar System

“…Different scenarios have been proposed to explain the abundance of the SLRs in the ESS but a global astrophysical interpretation accounting for all of them is still lacking (see Wasserburg et al 2006 for a recent review). The possibility of producing SLRs by in situ irradiation has been extensively discussed and challenged in the last decade (Lee et al 1998;Gounelle et al 2001Gounelle et al , 2006Goswami et al 2001;Leya et al 2003), but all these studies addressed, above all, the issue of producing the canonical abundance ratios locally within a given target. Yet, a crucial issue is the total amount of nuclei that can be synthesized within such a process.…”